1. Field of the invention
This invention relates generally to high heel shoes and, more particularly, to high heel shoes with detachable heels.
2. An analysis of the prior art as related to the developmental history of the invention.
The invention in its present form was developed as a result of research into the problems associated with making high heel shoes with detachable heels that can also function as low or flat heel shoes. In investigating this problem, it became apparent that high heel shoes as they are currently manufactured can not be made to function as low heel or flat shoes when the heels have been removed. This is because high heel shoes have a very rigid arch structure permanently built in to them which does not go away if the heels are removed or broken off. A shoe in this configuration is unwearable for any reasonable walking motion without the heels. Conversely, flat heel shoes can't be modified to work as high heels. If high heels were attached to a conventional flat shoe, the result would be a very unstable shoe that would not stand up in the high heel position when worn. This is because flats are much more flexible than high heel shoes and any movement would cause the section of the shoe attached to the high heels to twist and the heels would collapse.
It was theorized that if a rigid, hinged-sole shoe could be built that would work comfortably as a flat, such a shoe would also provide a stable platform to which high heels could be attached because a hinged-sole shoe design could be built to be very laterally stable thus preventing the problem of heel collapse described above when high heels are attached to conventional flats.
Various hinged sole constructions with single and multiple hinge lines were attempted and none of the initial designs worked but it was noted that one prototype with a single hinge line running perpendicular to the length of the foot and in the general area of the ball of the foot exhibited a curious tendency to twist against the sandal straps when attempting to walk, as if the shoe were trying to align itself with some natural, built-in hinge line in the wearer's foot. To further research this phenomenon, a special test rig was made where there was a lot of surface area for the foot to slide around on near the hinge and elastic straps held the foot to the sole such that this twisting motion could be explored. It was found that any wearer's foot will automatically line up with a hinged sole construction in an exact way that can be defined precisely with regards to the anatomy of the foot of the wearer.
There are five bones in the foot called the metatarsals which project forward and downward toward the toes as shown in FIG. 7A. These long thin bones each have an approximately ball-shaped terminus at their forward-most end and these bulbous forward terminating points for the metatarsal bones are referred to as the metatarsal heads. It was found that for any walking or standing motion, the foot aligned itself with the hinged sole such that the hinge line 30 ran directly underneath the lowest or weight-bearing point of the first metatarsal head 31 (the one connecting to the big toe) and the lowest or weight-bearing point of the fifth metatarsal head 32 (the one connecting to the smallest toe). Further analysis showed that this is consistent with certain things already known about the weight-bearing function of the foot. A tripod is one of nature's most efficient weight-bearing designs and when standing still, the foot functions as a tripod with the weight from the leg coming down to the ankle area where it is distributed rearward to the heel and forward to the lowest points of the first and fifth metatarsal heads.
The human skeletal structure is designed to support body weight and the metatarsals form the forward structural support for the foot and thus no other weight bearing points are possible. Experimentation confirms the theoretical analysis that any normal, properly functioning foot will flex along a line which runs under the lowest points of the first and fifth metatarsal heads during walking or when standing in the high heel position. This is a universal condition not subject to variation from individual to individual.
Most shoes have a generally elliptical shape and in a shoe of such design, there was found to be a geometrical relationship which consistently matched the anatomical relationship just described. To derive the geometrical construct as shown in FIG. 8, the shoe perimeter must be placed flat on a surface between two parallel lines 5 & 6 such that each parallel line touches the perimeter at only one point and the distance between the parallel lines is at a maximum. A line drawn through these two points defines the long axis 7 of the shoe. If a line is drawn parallel to the long axis touching the perimeter at only one point, that point being on the side closest to the other foot, that point will be defined as the most medial point on the sole perimeter 8. If another line is drawn parallel to the long axis touching the perimeter at only one point, that point being on the side furthest from the other foot, that point will be defined as the most lateral point on the sole perimeter 9. In a typical shoe of generally elliptical shape, the natural hinge line of the foot will coincide with a line passing through the points most lateral 9 and most medial 8 on the sole perimeter.
All further prototypes were built with a single hinge line oriented in exactly this way and, as a manufacturing expedience, the rear portions of the sole were made to be absolutely planar. The sole construction has a forward section with an upper and a lower surface, a rear section with an upper and a lower surface and a straight hinge line joining both sections in the manner described above anatomically and geometrically such that when the shoe is upright on a flat surface(the ground), the upper surfaces of the forward and rear sole sections along the hinge line are at the same height above the ground. Subsequent testing proved that the design did indeed work very well as both a high heel shoe and as a flat shoe. Even though the sole of the design is absolutely rigid, being made out of aluminum which will not bend at all and which only flexes along the hinge line, it was found that when worn as flats, the shoes felt exactly like regular flat shoes with no inhibiting sensations or restrictions to movement of any kind. A most unexpected result which took a long time to research and explain, however, was the fact that wearers of the prototypes in their high-heel configuration often commented very strongly about how comfortable these shoes were as high heels, expressing the view that they were much more comfortable than conventional high heels as the wearers had previously experienced them.
It has long been known that high heel shoes as they have been manufactured to date are orthopedically unsound, being painful and damaging to the feet. This is because the built-in arch of conventional high heel shoes does not correctly match the anatomy of the human foot. The high heel shoe arch is used to provide a very rigid structure so that the high heels won't collapse when weight is applied downward on the heels. As mentioned already, if a high heel was attached to a flexible flat shoe and weight was applied in some direction other than straight down the middle of the heel, the heel would twist in relation to the shoe and foot and collapse, winding up pressed sideways between the foot and the ground. The conventional high heel arch is so stiff that this collapse will not occur but the shoe arch winds up working in a way that is painful and damaging to the arch of the wearer's foot.
A review of basic civil engineering principles shows that the purpose of an arch is to shift the point at which weight is applied. Thus, weight applied to the top middle of an arch will be diverted so that it comes down on the two end points of the arch, traversing the span under the middle of the arch without coming down through the middle of the span(arch). Arches are very strong when weight is applied down on the convex side but are very weak when weight is applied up into the concave side. As can be seen in FIG. 1, the arch is very strong and resistant to forces acting in a downward direction but if a significant force were applied in an upward direction into the arch, the bridge would be damaged, possibly seriously enough to cause structural failure.
FIG. 2 shows a human foot standing on a flat surface. The weight coming down from the leg is projected rearward onto the heel and forward onto the ball of the foot (the metatarsal head area). Notice how the area under the arch of the foot is clear of any contact with the ground so that no weight is felt there. If a hard object were to be placed under the arch of the foot so that the weight from the leg were to be transmitted through the arch against the hard object, the ability of the heel and ball of the foot to make firm contact with the ground would be interfered with and the woman whose foot is shown in FIG. 2 would experience considerable pain. This is exactly the effect that is experienced when wearing conventional high heel shoes.
The conventional high heel shoe's arch starts in the heel area and curves forward and down, generally reaching the ground behind the first metatarsal head. The arch curvature lifts the fifth metatarsal head off the ground so that it can't make firm contact with the ground. For high heel shoes with loose-fitting uppers such as high heel sandals, the first metatarsal head will often slide back against the shank but this exaggerates the tendency for the fifth metatarsal head to be lifted up off the ground. Forward of the arch, the shoe sole is flexible and this is where the shoe bends during walking. Thus, the arch of the shoe presses up into the arch of the foot, forcing the foot to bear weight in the sensitive arch area. The arch of the foot also rocks back and forth in this position against the arch of the shoe as weight is shifted from the heel of the foot to the ball of the foot during walking. This rocking motion also causes chafing of the foot against the uppers of the shoe, particularly causing friction and abrasion between the rear of the heel of the foot and the rear upper of the shoe. There is a misconception that has been held by some that the shape of the arch of the foot changes during the walking motion and that the arch of the foot has a different curvature when wearing high heel shoes than when wearing flats. This issue has been carefully researched and it has been found that there is a fixed planar relationship between the heel and the first and fifth metatarsal heads that remains constant when weight is applied on the foot. Thus, the planar relationship between the heel and the ball of the foot as shown in FIG. 2 is identical to the planar relationship between the heel and the ball of the foot in FIG. 3. The arch does not change shape and the distances between the heel and the first and fifth metatarsal heads remain constant regardless of whether the woman is standing flat as in FIG. 2 or up on her toes as in FIG. 3.
As an additional note, what is generally referred to as the arch of the foot is in fact a series of five arches adjacent to each other. The first metatarsal bone and the heel form part of the first arch which is the highest arch with the greatest curvature while the fifth metatarsal bone and the heel form form part of the fifth arch which is the lowest with the least curvature. When referring to the arch of the foot, what is meant is the bottom surface of the foot between the heel and the metatarsal heads. The woman in FIG. 2 has a particularly high arch as there is an air gap between her foot and the ground all the way from beneath her first metatarsal bone to beneath her fifth metatarsal bone. More typically, the flesh of the foot is in contact with the ground along the line below the fifth metatarsal bone. For someone who is flat-footed, the flesh of the foot is in contact with the ground below all the metatarsal bones.
Thus, the invention as described herein will perfectly track the motion of the wearer's foot whether walking, standing, dancing or merely at rest in the high heel position. If the invention were placed under the foot in FIG. 2, it would feel exactly the same as if nothing was there and the wearer were just standing barefoot on a smooth flat surface. If the foot in FIG. 2 were to rise up to the position shown in FIG. 3, the hinged sole would follow the motion of the foot, flexing exactly along the natural hinge of the foot wherein the first and fifth metatarsal heads (ball of the foot) remain in contact with the ground and the heel rises.
It should be noted that the first and fifth metatarsal heads aren't always both in contact with the ground at the same time. If the woman in FIG. 3 were to turn her body to her right with her feet where they are, the fifth metatarsal head of her left foot would leave the ground and more weight would press down on the first metatarsal head and toes of that foot. Nonetheless, the planar geometric relationship that exists between the first metatarsal head, fifth metatarsal head and heel that is the same in FIGS. 2 and 3 would be preserved in this other condition as well. As the woman twisted her body and the fifth metatarsal head of her left foot lifted up off the ground, the small toes would be lifted off the ground by the forward sole segment of the invention. Experiments have shown that wearers do not have any sensation of this and the shoes still feel perfectly natural. This is an important reason why the invention can be worn with no discomfort or inhibition of movement.
If the invention in its high heel configuration were fitted to the foot in FIG. 3, and the wearer were to stand at rest in the high heel position, the following significant orthopedic advantages over conventional high heel shoes would be experienced. No pressure would be applied up into the sensitive arch area of the foot and the natural weight bearing characteristics of the foot as seen in FIG. 2 would be very closely preserved. The first and fifth metatarsal heads(ball of the foot) would be provided firm, uninhibited contact with the ground and the heel of the foot would rest against the inclined rear planar section of the invention in exactly the same way it would contact'the ground in FIG. 2. Also, the ball of the foot would have a supportive surface to rest against both forward of and to the rear of the hinge line. In conventional high heel shoes, the arch starts in the heel area and curves forward and down, generally reaching the ground behind the first metatarsal head. This results in a lack of support in this area which is why women wearing conventional high heel shoes experience pain in the ball area of the foot as well as in the arch area of the foot. Quite a few women who have worn the prototypes in their high heel configuration have commented that the shoes "massage" the ball of the foot while walking, providing a very pleasant supportive sensation in that area whereas conventional high heel shoes cause an exaggerated strain to be present in that area. This additional support in the ball area of the foot also eliminates the tendency of conventional high heel shoes to cause the toes to be shoved forward against the upper of the shoe. Thus, conventional high heel shoes apply pressure in an area that they shouldn't which is the arch of the foot but fail to provide the necessary supporting pressure for the ball of the foot which needs a firm surface to rest against.
In fact, the term "arch support" is really a false concept. In a flexible-soled flat shoe, cushioning is needed under the arch to protect the sensitive arch area from the intrusion of hard objects that one might step on but this cushioning acts as a barrier to penetration and not as a support to hold up the arch. The arch of conventional high heel shoes is there to stiffen the shoe so the heels don't collapse but totally violates the correct orthopedic condition of the foot. The invention provides a rigid sole section that will act as a perfect barrier between the foot and the ground when the shoe is in the flat heel configuration and thus no padding is needed to push up into the arch of the foot to provide protection from foot impact with such objects as rocks or irregular walking surfaces.
Above are summarized orthopedic advantages of the invention with regards to pain experienced in the foot but another attribute of the invention greatly reduces pain experienced in the lower back. When the foot is flat on the ground as in FIG. 2, the bottom of the heel faces downward but when the heel rises as in FIG. 3, the bottom of the heel not only faces downward but also faces in a medial direction toward the other foot. Thus, during a natural walking motion, as the heel rises it also tilts such the bottom of the foot on the medial side of the heel area is higher up off the ground than the bottom of the foot on the lateral side of the heel area. Conventional high heel shoes do not take this tilt into account as can be seen in FIGS. 4 and 5 of F. T. Romano, U.S. Pat. No. 2,707,341 dated May 3, 1955. FIG. 4A of this application shows the view from the rear of the left heel of this invention and it correctly matches the natural foot alignment shown in FIG. 3. The heel itself is vertical but the top has been inclined to support the rear planar sole section of the invention at the angle it assumes in the high heel position. FIG. 4B shows the view from the rear of the right heel. To demonstrate the effect involved, stand with both feet as in FIG. 3 and then twist both heels into a vertical alignment as is required to wear conventional high heel shoes. Experiments indicate that allowing the foot to rest in the high heel position with the natural medial to lateral tilt of the heel shown in FIG. 3 supported by a sole surface that tilts as shown along the top of the shoe heel in FIG. 4A results in most of the lower back pain associated with conventional high heels being eliminated.
Another significant comfort advantage of the invention over conventional high heel shoes is the stability provided by the rigid hinged connection between the rear sole section and the front sole section. This feature allows balancing forces from the toes to be applied against the forward sole section to aid in controlling instability of the shoe that will occur when wearing a high heel. In conventional high heel shoes, the rear section with the arch is very rigid and contacts the ground behind the first metatarsal head which rests on a flexible section. This results in unwanted flexibility between the area of the sole under the ball of the foot and the surface below the arch and heel of the foot. Thus, the toes can not exert a balancing force that will stabilize a wobbling heel. As was mentioned earlier, there is a fixed relationship between the ball and heel of the foot but conventional high heel shoes do not incorporate this geometry into their design and thus the foot and shoe wobble in relationship to each other as the foot seeks out a stable platform while walking or standing. This effect comes from the inability of the heel and ball of the foot to simultaneously bear weight properly due to the incorrectly arched surface of the shoe sole and also due to the tendency of the feet to tilt laterally as in FIG. 3 while the shoe tries to twist the feet so that the heels will be perfectly vertical. The invention incorporates the correct medial to lateral tilt of the heel area of the foot and a rigid coupling between heel and ball of the foot so wobbling of the foot and shoe is eliminated. Eliminating this motion between foot and shoe also eliminates the chafing that occurs in conventional high heel shoes between the foot and the upper of the shoe.
During a normal walking motion, the heel rises from zero height as seen in FIG. 2 to some maximum height at which point the ball of the foot leaves the ground. The larger the shoe size, the higher the heel rises before the ball of the foot lifts and this maximum heel elevation during a normal walking motion wherein the ball of the foot is still firmly planted on the ground as in FIG. 3 is the effective maximum heel height at which the invention will still be orthopedically effective. For an average size foot, five inches heel height is about the maximum height at which the orthopedic advantages described above will still be experienced. For heel heights less than one inch high, the differences between the invention and a conventional shoe are negligible and thus the invention is specified as being effective when the attached heel raises the rear sole section such that it rises between one and five inches, such rise being measured as the difference in elevation between the lowest point of the upper rear sole surface(at the hinge) and the highest point of the upper rear sole surface(behind the back of the heel).
Patent searches revealed a large number of shoe designs with hinged soles. Reviewing this prior art, it is seen that virtually every possible hinged shoe arrangement has been described with single and multiple hinge assemblies shown with a wide range of hinge positions and hinge orientations. Many of the prior art examples were recognized as early prototype design attempts that were experimented with and found not to work. As was described above, the inventor discovered through extensive experimentation that there is one and only one rigid hinged sole assembly that will allow for proper foot movement. The only prior art example that shows this correct design is Danish Patent # 20574 dated Sep. 8, 1915 by D. Kapskobund and therefore, the Kapskobund design was closely analyzed to see what its intended function was.
The Kapskobund shoe is clearly seen to be a standard European clog which has been modified by the insertion of a hinge which is spring-loaded in the non-flexed(flat sole) position by two springs below the upper surface running parallel to the long axis of the clog. Historically, clogs were developed for use in the north coastal areas of Europe such as Holland and Denmark where the ground is often wet with standing water forming large puddles in the lowlands. The purpose of clogs is to provide a high platform shoe made out of wood which keeps the foot elevated above puddles and which insulates the foot against wetness. In the past, the Japanese also developed clogs which they called "geta" for the same purpose. The dynamics of the walking motion when wearing clogs can be analyzed with the help of FIGS. 5A and 5B showing a side view of Japanese geta which work the same as European clogs. A foot rests against the top of the clog in FIG. 5A in the same orientation as the foot in FIG. 2. When walking forward, the clog rocks down into the position shown in FIG. 5B and also, the clog rotates such that the front of the clog points slightly away from the other foot and the back of the clog points slightly toward the other foot. What the clog motion is trying to accomplish is to simulate the position of the foot in FIG. 3 but this can only be approximated because the foot can't bend along the metatarsal hinge line shown in FIG. 3. To make up the remaining flexion of the foot, the back of the foot rises slightly away from the rear sole section of the clog. This completes the motion and enables a free walking movement with clogs. In order to permit the back of the foot to rise away from the rear sole section of European style clogs, the back section of the upper on those clogs is open, exposing the heel of the foot. On Japanese geta, the entire upper is open, using only sandal thong straps.
The obvious disadvantage to such a design is that the upper must be open at least in the back, exposing the heel of the foot to possible cold and wet conditions. If the clog is given the ability to flex just a little along the natural metatarsal hinge line, the surface of the foot can stay in contact with the sole of the shoe throughout any walking motion and this would enable a clog-type shoe to be made with completely enclosed uppers such as those used on boots, for example. A close look at Kapskobund's patent shows that this is exactly what was intended with this design. In FIG. 1 of Kapskobund, the letter "v" points to an indentation or offset that goes all the way around the perimeter of the upper part of the clog. This recessed indentation is where the leather upper fits and is fastened to the wooden bottom of the shoe. In a normal clog, the offset area would not extend around the back of the clog as indicated by the rearmost "v" because that area would not have an upper attached there.
In order for a clog to perform its function of keeping a foot high and dry off the ground and yet also provide for free and easy movement, the clog must be capable of rocking down into the position shown in FIG. 5B. This requires an angled or curved lower surface to the front section of the clog. When walking, the forward-most(and highest) point of the lower surface of the front section of the shoe rocks down to contact the ground, raising the heel and facilitating the walking movement. In order for the clog to be stable when standing on it so it won't unintentionally flip back and forth between the conditions shown in FIGS. 5A and 5B, certain geometrical constraints must apply.
These geometrical constraints can be seen in FIG. 6. The vertical rise 3 of the upper surface of the rear sole section which is the difference in height between the highest point 2 on that surface and the lowest point 1 on that surface must be less than the height 4 of the highest (forward-most) point of the lower surface of the front section of the shoe. Otherwise, a see-saw effect would occur between the positions seen in FIGS. 5A and 5B. The exact opposite relationship must exist in high heel shoes as designed conventionally or in the form of the invention. Stability in that case would have to be achieved by using a thin sole structure in combination with a reduction of the curvature of the bottom surface of the front section of the shoe. A shoe thus stabilized will no longer provide the functional raised-sole effect of clogs and thus these two types of shoes have a mutually converse property which makes them distinct and separate from each other.
It is possible to create platform high heel shoes but in reality they function just like stilts and nothing can be done with such a design to introduce stability or comfort. If high heels were attached to any clog(Kapskobund's design included), the clog would have no stability for standing or walking movements and would be dysfunctional, tending to remain in the position shown in FIG. 5B most of the time.
The patent searches also revealed numerous prior-art high heel shoe designs that claim to be capable of functioning with heels of different height. All of these designs have a conventional high heel arch shoe structure and except for the U.S. Patents to M. J. Dill (No. 4,670,996 dated Jun. 9, 1987) and F. T. Romano (No. 2,707,341 dated May 3, 1955), no mention is made of how to deal with the problems associated with a shoe sole structure making the transition between heel heights. Dill addresses this problem with the solution of a collapsible shank that retracts into a slot in the forward part of the shoe's sole. Apparently, this design presumes that the foot changes length when the heel height is changed. As was mentioned previously, however, and as is shown in FIGS. 2, 3, 7A, and 7B, there is a constant geometric relationship between the heel of the foot and the ball of the foot when weight is applied to the foot.
In all the prior art high heel shoe designs, the shank has a built-in curvature which can not be eliminated which is similar to the curvature found in conventional high heel shoes. Thus, those designs will not work for low heel shoes and will induce the same orthopedic discomfort found in conventional high heel shoes wherein unwanted stress will be imposed on the sensitive arch area of the foot, the ability for the ball and heel of the foot to bear weight naturally will be impeded and the heels will be twisted out of natural alignment resulting in lower back pain.